The present disclosure relates to a fixing device which fixes a toner image on a sheet and an image forming apparatus including the fixing device.
An image forming apparatus, such as a copying machine and a printer, is provided with a fixing device which fixes a toner image transferred on a sheet to the sheet. The fixing device includes a fixing roller heated by a heat source and a pressing roller which is pressed against the fixing roller to form a fixing nip between the fixing roller and the pressing roller. At the fixing nip, the toner image is heated and pressed to be fixed on the sheet.
Both end portions of the fixing roller are supported by bearings in a rotatable manner via heat insulating members. Because the fixing roller is heated by the heat source to a predetermined high temperature, the heat insulating member is made of high heat insulation material and prevents the heat from being transmitted to members disposed near the fixing roller.
The fixing roller rotates at a high speed during a fixing operation and at a row speed during a waiting period. When the fixing roller rotates, the heat insulating member and an inner ring of the bearing are rotated together with the fixing member. However, because a clearance is formed between the end portion of the fixing roller and the heat insulating member, the heat insulating member is sometimes slid with respect to the end portion of the fixing member. Then, an abnormal noise may be occurred owing to friction at the sliding. In this case, if the heat insulating member has a high rigidity in its circumferential direction and fastens the end portion of the fixing roller tightly, the friction becomes large and the abnormal noise may be easily occurred. Additionally, because an outer diameter of the end portion of the fixing roller is varied by heating and cooling of the fixing roller, the clearance between the end portion of the fixing roller and the heat insulating member may be varied.
Then, the heat insulating member is sometimes formed with a slitting groove extending in an axial direction of the heat insulating member. The slitting groove absorbs the outer diameter variation owing to expanding and shrinking of the fixing roller caused by the heating and cooling.
However, if the slitting groove is formed in the heat insulating member, it is difficult to lower the circumferential rigidity of the heat insulating member sufficiently and to prevent the abnormal noise occurred when the heat insulating member fastens the end portion of the fixing roller tightly. Additionally, if the heat insulating member is applied with a lubricant, such as a grease, a sliding performance of the heat insulating member may be improved. However, because of application irregularity or scattering of the grease, it is impossible to secure sufficient durability.